Excitonic photoluminescence in semiconductor quantum wells: plasma versus excitons.

Time resolved photoluminescence spectra after monresonant excitation show a distinct 1s resonance, independent of the existence of bound excitons. A microscopic analyis identifies excition and electron-hole plasma contributions. For low temperatures and low densities, the excitonic emission is extremely sensitive to details of the electron hole pair population making it possible to identify even minute fractions of optically active excitons.